Cysteine-Mediated Intracellular Building of Luciferin to Enhance Probe Retention and Fluorescence Turn-On.

The development of sensitive and selective small molecular probes that enable real-time detection of endogenous cysteine (Cys) has become an attractive topic because of the essential roles played by Cys in controlling the cellular nitrogen balance and in maintaining biological redox homeostasis. Herein, we report a Cys-specific probe, 2-cyanobenzothiazol-6-yl acrylate (CBTOA), that shows not only fluorescence turn-on for sensitive detection of endogenous Cys but also enhanced probe retention inside cells for real-time monitoring of Cys levels upon external stimulation. Cys-mediated intracellular formation of luciferin from CBTOA was the key strategy leading to this new type of fluorogenic probe. CBTOA showed fast response to Cys in living cells and liver tissue slices with high sensitivity and selectivity. By using CBTOA as a real-time probe, we were able to monitor the change in Cys levels in living HeLa cells under ROS-induced oxidative stress as well as in human mesenchymal stem cells during adipogenic differentiation.